For instance, motorcycle tires for running on rough terrain for using motocross or the like include a tread portion provided with a plurality of blocks. When these tires travel on off-road such as sandy, soil or muddy road, the blocks can bite the road to maintain grip performance.
In general, the blocks are molded using a recess of a mold through a vulcanization process. In the vulcanization process, tread rubber around blocks flows significantly. Such a significant rubber flow may cause a problem that a tread rubber thickness tends to be thin locally around the blocks and deteriorates durability of the blocks.
Furthermore, when traveling, a large stress and bending moment acts on the base portion of the respective blocks. Thus, there was a problem that damage tends to concentrate the base portion of the blocks.
In order to improve durability of tread blocks, the following patent document 1, for instance, has proposed a motorcycle tire for running on rough terrain having an improved shape of a base portion of a block.